The present invention relates generally to a piston defining a combustion chamber for an internal combustion engine and, more particularly, to such a device in which fuel is effectively mixed to activate the combustion state at a latter period of combustion.
As shown in FIGS. 9 and 10, in a combustion chamber 22 of a conventional internal combustion engine, peripheral wall 24 provides a substantially square contour in the center of a crown portion of a piston 2. An upwardly projecting conical portion 26 is provided at the center of a bottom wall 25, and the peripheral wall 24 has a narrowed edge portion 23. Fuel is injected obliquely from the center on the upper side of the combustion chamber 22 against the square peripheral wall 24. Such a combustion chamber for an internal combustion engine as described, for example, in Japanese Patent Laid-Open No. 62-157221.
In the aforementioned construction, a change in time of the combustion cycle is represented by a crank angle, as indicated by curve 29 in FIG. 11. The heat generation rate existing while fuel moves in an intake swirl x at an initial period of combustion is high, whereas at a latter period of the combustion cycle, fuel impinges upon the peripheral wall 24 of the combustion chamber 22 and is adhered thereto completely unburned. Therefore, the heat generation rate is reduced significantly. During the initial period of the aforementioned combustion cycle, excessive heat is generated to cause engine knocks, whereas during the latter period of combustion when lesser amounts of heat are generated, black smoke resulting from incomplete combustion of fuel is produced. Injection of fuel under high pressure is effective to reduce the rate of black smoke production but it also tends to increase engine knock. Consequently, it is difficult to simultaneously limit both engine knock and the production of undesirable black smoke. Improved performance would be obtained by increasing combustion during the latter period of the combustion cycle as indicated by line 30 in FIG. 11.
It is the object of the present invention, therefore, to provide a combustion chamber defining piston for an internal combustion engine which can disturb the motion of combustion gases or flame to promote the combustion of fuel.